Thermodynamic destabilization and kinetic optimization for the de-/hydrogenation of Mg₈₅Ni₁₅ alloy by tailoring Mg(In) and Mg₂Ni(In) double solid solution

To increase the hydrogen de-/absorption rate and reduce the stability of MgH₂, element indium (In) is introduced into the hypereutectic Mg₈₅Ni₁₅ alloy. The results show that solid solution phases of Mg(In) and Mg₂Ni(In) are formed simultaneously, and the lattice parameters of Mg crystals decrease while that of Mg₂Ni crystals increase. The hydrogen storage capacity of Mg₈₅Ni_14.5In_0.5 alloy reaches 3.5 wt% at 125 ℃ with the hydrogenation rates accelerated significantly, which is higher than the 2.4 wt% of Mg₈₅Ni₁₅ alloy. For dehydrogenation, Mg₈₅Ni₁₄In_1.0 hydride can release 4.1 wt% hydrogen at 225 ℃ in 15 min. The main peak temperature in DSC test for dehydrogenation is decreased to 226.6 ℃ of Mg₈₅Ni_13.5In_1.5 hydride from 246.1 ℃ of Mg₈₅Ni₁₅ hydride and decomposition enthalpy (ΔH) of Mg₈₅Ni_13.5In_1.5 hydride is decreased to 60.9 kJ/mol. The rapid hydrogenation rate is owing to the dissolved In atoms in Mg₂Ni lattice causing lattice expansion, which acts as fast diffusion path for hydrogen atoms. In Mg(In)H₂ phase, the strong interaction between Mg and In weakens the affinity of Mg and H, which accounts for the reduced ΔH of Mg(In)H₂. The weakened strength of Ni-H bond in Mg₂Ni(In)H₄ also results in the decreased stability of hydride.